In certain criminal investigations, "known" biological samples (primarily blood, saliva, and semen) are collected from victims, suspects, and their relatives. In these criminal investigations, "unknown" biological specimens are also collected, generally from the crime scene and from residences, automobiles, and other items associated with one or more suspects in the investigation. These unknown biological specimens are often scrapings of drops of blood, saliva, semen, or small tissue fragments.
Both known and unknown biological specimens are subjected to various analyses, including characterizations of their constituent deoxyribonucleic acid (DNA). The standard analysis methods used are (a) analysis of Variable Numbers of Tandem Repeats (VNTR), (b) analysis of Short Tandem Repeats (STR), (c) analysis of Single Nucleotide Polymorphisms (SNP), (d) analysis of Restriction Fragment Length Polymorphisms (RFLPs), and (e) analysis of mitochondrial DNA sequences. VNTR and STR analyses utilize simple or multiplex Polymerase Chain Reaction (PCR) technology; RFLP analysis utilizes restriction enzyme digestion of DNA followed by DNA hybridization techniques with labeled DNA probes; and mitochondrial DNA sequence analysis utilizes a combination of PCR technology and conventional dideoxy ("Sanger") sequencing in a process known as cycle sequencing.
Results from the above analyses are used to compare the known and unknown samples to determine any possible relationships between the samples.
However, problems may arise due to the deliberate or inadvertent contamination of unknown biological samples by previously collected known biological samples, or by subsequent samples due to the confusion of samples (e.g. during analysis). In the example of criminal forensic analysis, such contamination could arise when blood from a victim is collected at a particular location, then transported to the residence of a suspect and subsequently released at the suspect's residence.
Thus a need exists for a mechanism whereby collected known biological samples would be unambiguously marked and identified at the time of collection. Then, if a marked sample should happen to contaminate another locale, the sample would be recognized as a contaminant upon subsequent analysis. This would also safeguard against the confusion of samples during analysis, preventing a "known" sample from being mistaken as a sample collected from a crime scene.